FIG. 1 is an electrical schematic drawing showing the basic combination of a three-phase bridge inverter and a three-phase motor to form a drive circuit 10 for an electrically powered vehicle. The circuit 10 of FIG. 1 includes a three phase bridge inverter 12 (including a DC bus input capacitor Ci), a battery 14, and a three phase motor 16. The inverter is formed from six transistors arranged as three pairs of switches: Q1 and Q2, Q3 and Q4, and Q5 and Q6, each forming a switching pole with a corresponding phase node (18a, 18b, 18c) at its center. Each phase (Phase A, Phase B, Phase C) provides power from the inverter 12 to the motor 16 and is coupled to a corresponding phase node.
Three existing transformerless integrated drive-recharge schemes are known in the art as illustrated in FIGS. 2, 3 and 4. For each of these schemes, the starting point is the combination of a three-phase, voltage-fed inverter coupled with a three-phase motor as shown in FIG. 1. In each scheme, the motor type may be induction, brushless permanent magnet, or a synchronous reluctance. In each scheme, switch-mode power conversion with boost-mode action is used during recharge. The motor winding is used as an inductive circuit element. Accordingly, for each of these schemes, the peak of the input recharge voltage must be less than the battery voltage.
FIG. 2 is an electrical schematic drawing showing an integrated recharge circuit 20 using a diode bridge.
With the FIG. 2 scheme, a diode bridge 24 and conventional EMI (electromagnetic interference) filter/recharge port 26 are added to the FIG. 1 inverter-motor 10 to provide the recharge function. Diode bridge 24 and filter 26 are coupled to inverter-motor 10 with lines 28 and 30 (ground line G). When operated in the drive-mode, each of the diodes within diode bridge 24 remain back-biased at all times thus effectively disconnecting filter 26 from the inverter-motor combination and thereby preventing unwanted currents within filter 26 during drive-mode operation.
When operated in recharge-mode, input power (single-phase or three-phase) is rectified by diode bridge 24 to provide a pulsating DC (Direct Current) voltage source. In turn, this voltage source is then boosted to deliver power to battery 14. The boost action is provided by conventional pulse width modulation (PWM) control of semiconductor switches Q3 through Q6 in combination with inductance provided by the motor windings. Switches Q1 and Q2 remain off during the recharge-mode. Control of Q3 through Q6 can be such that odd-numbered current harmonics within the DC bus cancel—thus minimizing losses within capacitor Ci.
By using a control function where current ix is maintained proportionate to voltage vx, recharge power factor is optimized. With single-phase power, near unity power factor can be maintained and where three-phase power is used, the power factor degrades only to approximately 96%.
Maximum recharge power is typically established by the motor rating. For single-phase operation with this approach, the maximum continuous recharge power is approximately one half of the continuous drive-mode rating. For three-phase operation, the continuous rating jumps to about 70% of the continuous drive rating.
The scheme shown in FIG. 2 is advantageous in that it provides elimination of contactors, insurance of uni-directionality (power cannot return to the utility), and ability to operate from any AC (Alternating Current) power source (such as a utility) having a peak voltage lower than the battery voltage. Some disadvantages of this approach include the addition of cost and power loss due to the diode bridge, inability to control reactive power, inability to provide bidirectional operation (returning power to the utility), degradation of power factor when operated with three-phase power input, and presence of a high common-mode voltage between line 30 (the return) and the time average of lines X, Y and Z. Because the size of the common-mode filter is proportionate to the common-mode voltage, this means that a moderately large common-mode filter must be used to prevent unwanted common-mode line currents.
FIG. 3 is an electrical schematic diagram showing an integrated recharge scheme 32 which uses a contactor K2 to open one phase leg. With this scheme, two contactors (K1, K2) and a conventional EMI filter/recharge port 26 are added to the FIG. 1 inverter-motor 10 to provide the recharge function. When operated in the drive-mode, contactor K1 is open and contactor K2 is closed—thus reestablishing the FIG. 1 configuration.
In the recharge-mode, K1 is closed and K2 is open, while Q1 through Q4 provide synchronous rectification; motor leakage inductance inherent in the motor is used to provide the required phase port inductance. Various PWM control schemes can be employed. In one scheme, control is such that line current is maintained instantaneously proportionate to line voltage—thus providing unity power factor operation.
As before, maximum recharge power is usually determined by the motor rating. Typically, the maximum continuous recharge power with this approach is approximately one half of the continuous drive-mode rating.
Advantages of the FIG. 3 scheme include elimination of added semiconductor components (e.g., the diode bridge 24 from the FIG. 2 scheme), ability to operate from any utility having a peak voltage lower than the battery voltage, capability of bidirectional operation (returning energy to the utility), ability to provide stand-alone AC power output, and ability to control reactive power. Disadvantages of this approach include a requirement for a relatively large common-mode filter due to absence of inductance associated with phase A of motor 16, a requirement for a relatively large contactor (K2) to handle full motor current during drive-mode operation, and an inability to accommodate three-phase power input at the Recharge Port. The physical size of the common-mode filter is proportionate to the product of the common-mode voltage and the RMS port current. The actual size of the common-mode inductor will depend upon details such as core material, heat transfer, and winding packing factor. A typical proportionality constant is in the range of 25 g/kVA to 100 g/kVA.
FIG. 4 is an electrical schematic diagram showing an integrated recharge scheme 40 with a two-pole contactor K2 to open a motor neutral “splice”. With this scheme, no neutral splice is provided within the motor; both legs of each of the three motor windings are brought out. Two contactors (K1, K2) and a conventional EMI filter/recharge port 26 are added to the FIG. 1 inverter-motor 10 to establish the recharge function. When operated in the drive-mode, contactor K1 is open and two-pole contactor K2 is closed—thus reestablishing the FIG. 1 configuration.
In the recharge-mode, contactor K1 is closed and contactor K2 is open, while Q1 through Q6 provide synchronous rectification; motor leakage inductance is used to provide the required phase port inductance. Various PWM control schemes can be employed. In one such scheme, control is such that utility line currents for all three phases are maintained instantaneously proportionate to corresponding line voltages—thus providing unity power factor operation.
As before, maximum recharge power is generally determined by the motor rating. Typically, for single-phase charging with this approach, the maximum continuous recharge power is approximately 50% of the continuous drive-mode rating. For three-phase charging, the continuous rating jumps to about 80% of the drive-mode continuous rating.
Advantages of this approach include elimination of semiconductor components (e.g. the diode bridge 24 of FIG. 2), elimination of the motor neutral splice, ability to operate from any utility having a peak voltage lower than the battery voltage, ability to accommodate both single and three-phase utility power, capability of bidirectional operation, ability to provide stand-alone single phase and three phase AC power output, ability to control reactive power, and reduction of recharge common-mode currents due to topology symmetry—thus enabling the use of a smaller common-mode filter. Disadvantages of this approach include a requirement for a relatively large contactor (K2) which handles full motor current during drive-mode operation, and a requirement for six large motor lines in place of three large lines.